At present, a long term evolution (LTE) system supports two types of duplex frequency division duplex (FDD) and time division duplex (TDD). LTE transmission includes transmission from a base station (an evolved nodeB (eNB)) to a user equipment (UE) (downlink (DL)), and transmission from the UE to the base station (uplink (UL)). In a TDD system, downlink and uplink are transmitted in a same carrier at different times, and in a FDD system, downlink and uplink are transmitted in different carriers.
FIG. 1 is a schematic diagram of an LTE TDD frame structure according to the related art.
Referring to FIG. 1, each radio frame is 10 ms long, and is equally divided into two half frames having a length of 5 ms each. Each half frame includes 8 timeslots having a length of 0.5 ms each and 3 special fields, i.e., a downlink pilot timeslot (DwPTS), a guard period (GP), and an uplink pilot timeslot (UpPTS). An overall length of the 3 special fields is 1 ms. Each subframe consists of two consecutive timeslots.
In an LTE system, when uplink data are transmitted on a physical uplink shared channel (PUSCH), a demodulation reference signal (DMRS) is required to estimate channels.
FIG. 2 is a schematic diagram of a PUSCH and DMRS configuration according to the related art.
Referring to FIG. 2, for a normal cyclic prefix (CP) configuration, 12 single carrier-frequency division multiple access (SC-FDMA) symbols are used as PUSCHs and 2 SC-FDMA symbols are used as DMRSs. For an extended cyclic prefix (CP) configuration, 10 SC-FDMA symbols are used for PUSCHs, and 2 SC-FDMA symbols are used for DMRSs. A DMRS sequence is generated from the following formula: rPUSCH(m·MscRS+n)=w(m)ru,v(α)(n), where m=0, 1, representing different SC-FDMA symbols at timeslot 0 and timeslot 1, and n=0, 1, . . . , MscRS−1, representing subcarriers for PUSCHs and DMRSs. ru,v(α)(n) represents the DMRS sequence, and a specific method of generating it may be seen in the version V8.9.0 (2009-12) of 3GPP TS 36.211. MscRS represents the number of subcarriers allocated to the UE for the PUSCHs, and α represents a cyclic shift (CS). Orthogonal cover code (OCC) w(m)(m=0,1) includes [w(0) w(1)]=[1 1] and [w(0)w(1)]=[1 −1].
FIG. 3 is a schematic diagram of a DMRS configuration of different UEs according to the related art.
Referring to FIG. 3, when PUSCH frequency-domain resources allocated to different UEs overlap completely, DMRSs adopting different cyclic shifts of a same Zadoff-Chu sequence are orthogonal, and DMRSs adopting different OCCs of a same Zadoff-Chu sequence are orthogonal too. When the PUSCH frequency-domain resources allocated to the different UEs overlap incompletely, DMRSs using different cyclic shifts of a Zadoff-Chu sequence are not orthogonal.
FIG. 4 is a schematic diagram of a DMRS configuration of different UEs according to the related art.
Referring to FIG. 4, DMRSs using different OCCs of a Zadoff-Chu sequence are orthogonal. However, if there are two SC-FDMA symbols in the time domain used as DMRSs, there will be only two orthogonal OCCs, and, when there are more than two UEs of uplink PUSCH shared resources, and PUSCH frequency-domain resources allocated for PUSCH of the UEs overlap incompletely, there will not be enough orthogonal DMRSs in the traditional art to make more UEs multiplex uplink physical resources. For example, in this case, when there are multiple UEs, the multiplexing ratio of the uplink physical resources will be relatively low.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.